“There is no evidence of any water quality issues at the Quabbin Reservoir following the trespassing incident,” said MWRA spokeswoman Ria Convery. “Any abnormalities are detected immediately.”

Concerns for potential terrorism were raised early Tuesday when a state police trooper spotted a group of seven people walking toward their car near the middle entrance to the reservoir. Quabbin closes to the public at sunset and all seven were considered to be tresspassing.

The group of five men and two women told police they were recent graduates of a chemical engineering program and were visiting Quabbin because it was in line with their studies and their career interests.

David Procopio, spokesman for the Massachusetts State Police, said there was no evidence that the group was engaged in terrorism or any crime beyond the trespassing charge.

Still, the state police contacted the Springfield office of the FBI as well as the Commonwealth Fusion Center, the state’s central hub for collecting and analyzing data related to possible terrorism.

State police also increased patrols at Quabbin and other water supplies around the state.

“Further investigation is being undertaken because of the late hour when they were observed, their curious explanation for why they wanted to see the reservoir and the fact that they were in an area marked no trespassing,” he said.

Special Agent Greg Comcowich, public affairs officer with the FBI office in Boston, said
the FBI is aid the state police in the investigation, but to this point there is no indication is was an act of terrorism.

“There is no apparent threat to public safety,” he said.

FBI involvement is “pretty standard” whenever there are potential threats to major infrastructure like reservoirs, the electrical grid or natural gas lines, he said.

The FBI will be conducting background and records checks of the seven people as part of what he called due diligence by investigators.

The names of the seven were not released. Each was summonsed to appear in court at a later date on a charge of trespassing. According to state police, they resided in Amherst, Northampton, Sunderland, Cambridge and New York City.

It is not clear when they were scheduled to appear in court.

Procopio said there were no warrants, detainers or advisories against any of the seven on record with Interpol, the FBI’s National Crime Information Center or with any state law enforcement agencies.

Daniel Fitzgibbons of the UMass-Amherst News Office said there was not much the campus could say about the matter, especially since the names of the people were not known and it could not be verified there was a UMass connection.

Quabbin, one of the world’s largest manmade reservoirs is roughly 39 square miles and, when full, can hold 412 billion gallons of water.

State Sen. Stephen Brewer of nearby Barre said the size of Quabbin makes it difficult to patrol “every second of every day.” Authorities are aided by people who fish on the reservoir who serve as “eyes and ears” for law enforcement.

Quabbin’s size also makes it somewhat impervious to contamination attacks.

“It would take a tanker truck, a 10,000-gallon tanker truck full of pesticides in concentrated form to violate the reservoir,” said Brewer.

Correspondent Jim Russell contributed to this report. Material from the State House New Service was used.